I actually had a passing acquaintance with the word "hoddydod," probably because of your writing. I just didn't know where it came from: I can understand "attercop," but this one really did look like a nursery rhyme.

"Ablaut reduplication" is the term I wanted, although the example I had in mind was "shilly-shally." I know reduplication and the concept of ablaut ("those scary little noises in the night," as my advisor calls the effect; for years, they gave Homeric scholars headaches) from Greek linguistics. I am never sure which concepts carry across languages and which ones don't.

Thanks!